Ticks in Maine
Ixodes scapularus (=dammini)
The "deer tick", officially known as the black-legged tick, is essentially the sole vector of the Lyme disease spirochete, Borrelia burgdorferi, as well as the agents of anaplasmosis, babesiosis, and deer tick virus. This tick's life cycle requires at least two years for completion.
Following its first appearance in southern Maine in the 1980's, this tick advanced along the coast and then inland, and may now occasionally be encountered in northern Maine. A mated adult female deer tick, having obtained a blood meal from a white-tailed deer, dog, cat, or other large mammal in the fall or early spring, may deposit up to 3000 eggs in late May and early June.
The Lyme spirochete is not passed from an infected female deer tick to her eggs. Uninfected larvae emerge in mid-summer and soon seek a blood meal, primarily from mice, other small mammals and certain songbirds. Many of the animals they feed on, particularly mice and chipmunks, will have been previously infected with the agents of Lyme and other tick-borne diseases; it is from these "reservoir hosts" that they become infected.
After over-wintering, larvae molt to nymphs which seek a second blood meal in the spring, passing on the infections they acquired as larvae to the next year's crop of small mammal/avian hosts.
Nymphs also feed on humans, dogs, and horses, and other hosts. Their tiny size and painless bites may allow them to remain undetected through the ~36 hours it takes for spirochetes to be transmitted from a feeding tick.
Most human Lyme disease results from the bite of undiscovered nymphs in the summer. Dogs and other furred animals are more frequently infected by adult ticks which escape detection. In Maine, nymphs peak in late June and July, which is when ~65% of the human cases of Lyme disease are reported. After repletion, deer tick nymphs drop to the leaf litter, and in early fall molt to adult males and females.
The "woodchuck tick", is widely distributed in Maine and is the second most common species of Ixodes found on people. It has not been associated with Lyme disease transmission. I. cookei usually feeds on wild animals, such as woodchucks , skunks, and raccoons, but will also feed readily on humans and domestic animals. This tick is known to be a vector of Powassan virus which causes severe encephalitis with high morbidity and mortality. Fortunately, chances of becoming infected with this virus are very low. The first reported case in the state was in 2000, and there have been four Maine-acquired cases reported since then.
The "squirrel tick", has not been associated with Lyme disease, but is a vector of Powassan virus. It will only occasionally bite humans.
This tick may be being displaced by I. scapularis. It is only occasionally found in Maine. Usually it feeds only on voles and mice, but it may bite humans, cats, dogs, and birds. A recent report indicates that it is a weak vector of Lyme disease, but no human cases of Lyme disease have been attributed to it. We have associated its bite with a reaction in cats, dogs and other domestic animals characterized by pain, swelling, fever, lethargy, and loss of appetite.
If you observe this reaction, we would like to receive the tick for identification. Please call us at (207) 396-8246 for arrangements.
This tick is usually found only on voles and mice and is common in many parts of Maine, but it is very rarely found on humans or domestic animals.
The American dog tick is not a vector of Lyme disease. This tick is particularly abundant in southwestern Maine, but its range has been expanding in recent years. Immature stages feed on voles and other small rodents, but adults are often found on humans, dogs, and other domestic animals. The adults, found from May through July but rarely later in the season, are larger than Ixodes ticks and can be distinguished by characteristic grayish-white markings. The tick is the vector of Rocky Mountain spotted fever in the eastern United States. No Maine-acquired cases of Rocky Mountain spotted fever have been confirmed to date. In the bar graph showing the seasonal abundance of adult dog and deer ticks, note that dog ticks are not active in October and November when adult deer tick activity is at it's peak.
The "winter tick," or "moose tick" is found on moose and deer and occasionally on horses, cows, dogs and humans, particularly in central and northern Maine. This is a one-host tick, so that once the larvae are on a moose in the fall, they feed and molt to nymphs, and then again to adults, resulting in huge numbers of ticks on moose by the end of the winter causing stress and anemia frequently resulting in death of the animal. Large numbers of the tiny larvae may be encountered by hunters in the fall, particularly in habitat where moose are found. This tick has not been associated with Lyme disease.
Also known as the "rabbit tick," I. leporispalustrus is usually found only on rabbits and birds. Although it has been reported to be rarely infected with Lyme disease bacteria, it does not transmit Lyme disease to humans.
The "Lone Star tick," is becoming more frequently found in Maine, most often on people traveling from states to the south where it is very common. The adult female is easily identified by the white spot on her back. This tick carries the agents of human and canine ehrlichiosis. It also transmits a spirochete (Borrelia lonestari) which in humans maybe associated with a rash and mild symptoms similar to Lyme disease.
The "brown dog tick" or "kennel tick," is widely distributed over the world, but only rarely found in Maine. It is commonly associated with dogs from large kennels. Dogs are the principal host. It has not been associated with Lyme disease transmission, but is the vector of canine ehrlichiosis which can be a debilitating illness in dogs.
Other species of Ixodes, I. brunneus (found on migratory birds), I. dentatus (found on rabbits and hares), I. uriae (found on marine birds), and I. gregsoni (found on mink, weasel and marten) are encountered in Maine, although infrequently. The bird tick Haemaphyhysalis chordeilis and Ixodes banksi (found on beaver and muskrat) may occur in Maine as well. There is no record of soft ticks, Family Argasidae, being collected in Maine.
Elsewhere in the country, ticks may carry other diseases, including tularemia and Q fever.
Top Row: Ixodes scapularis (dammini), the deer tick which transmits Lyme disease. Left to right: nymph, adult male, adult female, engorged adult female. Nymphs are most common May through July. Adults appear in the fall and early spring (graph).
Bottom Row: Dermacentor variabilis, the American dog tick, which is not thought to transmit Lyme disease. Left to right: adult male, adult female, engorged adult female. Adults are most common in May, June, and July. Note that the adult dog ticks are somewhat larger than adult deer ticks, and have characteristic white markings on the dorsal (top) side.
Photo by Jack Milton, Portland Press Herald